A turbine engine has a compressor section, a combustor section and a turbine section. In operation, the compressor section can induct ambient air and compress it. The compressed air can enter the combustor section and can be distributed to each of the combustors therein. FIG. 1 shows one example of a known combustor 10. When the compressor discharge air 12 enters the combustor 10, it is mixed with fuel supplied by a pilot nozzle 16 and a plurality of main nozzles 14 surrounding the pilot nozzle 16. Combustion of the air-fuel mixture 17 occurs downstream of the nozzles 14, 16 in a combustion zone 18, which is largely enclosed within a combustor liner assembly 20. As a result, a hot working gas is formed. The hot working gas can be routed to the turbine section, where the gas can expand and generate power that can drive a rotor. The combustor liner assembly 20 must be cooled to withstand the high temperature of the combustion occurring within. One particular area of the combustor liner assembly 20 that is subjected to some of the highest combustion temperatures is the downstream end region 22, which includes the downstream end 24.
One known manner of cooling the downstream end region 22 of the combustor liner assembly 20 is shown in FIG. 2. The downstream end region 22 of the combustor liner assembly 20 is typically formed separately from the rest of the combustor liner assembly 20. The downstream end region 22 of the combustor liner assembly 20 includes an outer cylinder 26 and an inner cylinder 28. The inner cylinder 28 is received in the outer cylinder 26, and the cylinders 26, 28 are joined together. The joined inner and outer cylinders 28, 26 are then joined to an upstream portion 30 of the combustor liner assembly 20. A spring clip 32 can operatively engage the outer cylinder 26 and an inner surface 34 of a transition duct 36, which routes the working gas to the turbine section.
Referring to FIG. 3, the inner cylinder 28 includes a plurality of fins 38 machined therein. An elongated, straight cooling channel 40 is defined between neighboring fins 38. The outer cylinder 26 includes a plurality of holes 42 near an upstream end thereof, as is shown in FIG. 2. The holes 42 can be distributed circumferentially about the outer cylinder 26. Each of the holes 42 is in fluid communication with a respective one of the cooling channels 40.
During engine operation, a portion of the compressor discharge air 12 is used to cool the downstream end region 22 of the combustor liner assembly 20. The compressor discharge air 12 enters the holes 42 in the outer cylinder 26, which meter the amount of air 12 that flows into the cooling channels 40. The air 12 passes along the cooling channels 40 between the fins 38, removing some of the heat by convection. The air 12 is ultimately exhausted out of the downstream end 24 of the combustor liner assembly 20. The air 12 joins the working gas flow in the transition duct 36, but it does not actively participate in the air/fuel mixture for the combustion process.
Such an arrangement has a number of drawbacks. For instance, the use of this air to cool the downstream end region 22 of the combustor liner assembly 20 takes away from its beneficial use elsewhere in the engine, such as to being available to burn in a fuel-lean mixture so as to help reduce NOx formation. Moreover, the straight cooling channels 40 are not optimized for convective heat transfer. Further, the inner cylinder 28 is expensive to fabricate. Additionally, there can be a gap between the inner cylinder 28 and the outer cylinder 26. Such a gap may arise due to manufacturing tolerances, misalignment during assembly and differential thermal expansion of the cylinders 26, 28 during engine operation. The size of the gap can vary during engine operation. Further, the size of the gap is often not uniform in the circumferential direction, which impacts the quality and efficiency of heat transfer and part life.
Thus, there is a need for a liner system that can minimize such concerns.